Process for the instantaneous peptization of polychloroprene latex

ABSTRACT

A PROCESS FOR INSTANTEOUS PEPTIZATION OF POLYCHLOROPRENE LATEXES MADE BY POLYMERIZING IN THE PRESENCE OF SULFUR AND A MODDIFYING AGENT SUCH AS IODOFORM OR A DIALKYLXANTHOGEN DISULFIDE, BY ADDING A SUITABLE THIOL AT A PH AT LEAST EQUAL TO 9.

United States Patent 3,808 183 PROCESS FOR THE INSTiANTANEOUS PEPTIZA- TION 0F POLYCHLOROPRENE LATEX Paul Branlard, Grenoble, and Jacques Modiano, Varces, France, assignors to DISTUGIL, Clichy, France No Drawing. Filed July 2, 1971, Ser. No. 159,536 Claims priority, appligzaggg grance, July 10, 1970,

Int. Cl. C08d N36 US. Cl. 26092.3 8 Claims ABSTRACT OF THE DISCLOSURE A process for instantaneous peptization of polychloroprene latexes made by polymerizing in the presence of sulfur and a modifying agent such as iodoform or a dialkylxanthogen disulfide, by adding a suitable thiol at a pH at least equal to 9.

The present invention relates to a process for instantaneous peptization of sulfur-modified polychloroprene latexes and new polychloroprene polymers obtained by such a process.

The sulfur-modified chloroprene latexes, according to the invention, are those obtained by aqueous solution polymerization of 2-chloro-butadiene-l,3 alone or in the presence of one or more copolymerizable monomers, in the presence of sulfur and of a modifying agent that can be for example iodoform or a dialkylxanthogen disulfide of the formula:

in which R; and R are alkyl groups containing from 1 to 8 carbon atoms. Preferred dialkylxanthogen disulfides are those in which R and R are alkyl groups containing from 3 to 4 carbon atoms such as diisopropylxanthogen disulfides.

Latex peptization such as is done according to the present invention can be defined as a partial or a complete dissociation of sulfur-modified polychloroprenes so as to provide more plastic products.

The principle of such a peptization is well known. It has been described in British Pat. No. 529,838 of Apr. 24, 1939 and French Pats. No. 1,376,314 of Dec. 5, 1963 and No. 1,393,099 of May 13, 1954. However, the processes used require the latex to be treated for several hours in the presence of tetraalkylthiuram disulfide mixed with a dialkyl ammonium dithiocarbamate of dialkyl at a temperature range of about 40 C. Besides, the process of manufacture itself is very difiicult because the peptization reaction which is slow is carried on during treatment of the latex so as to remove residual monomer and during rubber isolation phase. Moreover the plasticity of the rubhers so obtained varies with time, after peptization treatment properly so called, which constitutes a serious drawback for their use and their transformation into manufactured products.

An object of the present invention is to provide a process for the instantaneous pepetization of sulfur-modified polychloroprene latexes by treating such latexes having a pH at least equal to 9 with a thiol having a marked destructive ability towards the polysulfides linkages. One

3,808,183 Patented Apr. 30, 1974 such thiol has the general formula R-SH or its ionized sulfenyl form: RS-Me+ (Me being an alkali cation or ammonium) in which R may be as follows:

an alkyl group containing from 2 to 16 carbon atoms,

the chain of which is straight or branched, such as noctylmercaptan, n-dodecylmercaptan, amylmercaptan, t-butylmercaptan. The mercaptan can also consist of a mixture of alkylmercaptans having different alkyl groups;

an aryl or alkylaryl group such as thiophenol;

an arylcarbonyl group such as thiobenzoic and p-mercaptobenzoic acid;

an alkylcarboxy group such as mercaptosuccinic acid;

an alkylnaphthyl or naphthyl group such as thio-flnaphthol;

an arylthiazole or thiazole group such as mercaptobenzothiazole or its sodium salt;

an arylirnidazole or imidazole group such as mercaptobenzimidazole;

an alkylxanthate such as sodium isopropylxanthate.

These products can be introduced into the polychloroprene latex either in a pure state or in a solution or emulsion in a carrying liquid such as chloroprene or water or a mixture of these two compounds.

The principle of adding such compounds to latexes is already known. But in the processes known at the present time, the purpose of this addition and the function of the additives are essentially different from those of the present invention.

As a matter of fact, in the prior art, mercaptans added at the beginning of polymerization are used as chain transfer agents during polymerization but have no action on chains already polymerized. Other additives according to the invention, are known to be classical vulcanization agents.

On the other hand applicant has discovered surprisingly that the addition of such additives into sulfur-modified polychloroprene latexes, under determined pH conditions, generates a new function which is an instantaneous real 'peptization by breaking polymers chains already formed,

on a level with polysulfide chains, this leading to more plastic polymers. Analysis of the phenomena has shown that this immediate peptization is effected by the direct attack of the polysulfide bonds by the sulfenyl radical RS- without which there would be a reaction of the peptization agent with the residual modifying agent or their decomposition products. The sulfenyl anions have a marked action whatever may be the modifying agent used and which is active even in the absence of the modifying agent. The analysis of the dialkylxanthogen disulfide in the course of the polymerization has shown that this agent almost disappeared when polymerization stopped thus it cannot be a reaction between this agent and the peptizing sulfenyl agent. In the same way iodoform does not react upon the sulfenyl groups and phenomena analysis has shown that the peptizing agent reacts by breaking dior polysulfides bonds present in the polymer. It has been proved by the marked decrease of the polymer gel ratio after the polymer has been attacked, in the absence of a chain transfer agent. This peptizing action of the above cited thiols is the greater as the ratio of the sulfur combined with the polymer is greater.

Thereby the addition of such products so as to provide a maximum efficienc'y is done preferentially just at the end of polymerization. However, this addition can be effected during polymerization when the reaction has progressed enough and has already consumed the greatest part of the sulfur. The polymer formed is peptized instantaneously. But the progress of the polymerization is greatly slowed down. Thus there is a practical reason for adding this thiol just at the end of polymerization.

The modification of the Mooney viscosity of the latex is immediate and independent of the temperature in the range of from 5 to 80 C. It depends upon pH at the time of peptization having a minimeral value of 9, and the preferred pH of from 11 to 13. This Mooney viscosity is effective on the latex, whether the residual monomer is eliminated or not.

The proportion of thiol is from 0.05 to millimoles per mole of initial chloroprene monomer added. This proportion depends on the desired plasticity of the polymer so prepared, but also on the proportion of sulfur and dialkylxanthogen disulfide used in the reaction. The proportion of sulfur can vary from 0.01 to 2% by weight based on the chloroprene added. The proportion of modifying agent is from 0.5 to 4 milimoles per mole of chloroprene for dial'kylxanthogen disulfide and from 0.1 to 4 millimoles per mole of chloroprene for iodoform.

Owing to the fact that peptizing action is immediate and thorough, the Mooney viscosity of the polychloroprene does not develop further during manufacture treatment, which provides the advantage of easily preparing these rubbers having very reproducible Mooney viscosities.

Then the polymer can be isolated according to any known manner, for example by vapor entrainment of the latex under reduced pressure so as to remove the residual monomer, then by coagulation by cooling and drying in an oven having air circulation.

Sulfurand dialkylxanthogen disulfideand iodoformmodified polychloroprene rubbers are peptized instantaneously, according to the invention, and have a Mooney viscosity which allow their treatment in usual rubber apparatus without the need for a peptization step of the solid rubber during the mixing by addition of an appropriate peptizzing agent such as tetraethylthiuram disulfide alone or mixed with diphenylguanidine. Although such a treatment is not necessary, it is possible.

These rubbers have very good storage properties, better than those of sulfur-modified polychloroprene rubbers already known, and can be improved by an antioxidant addition. The antioxidant is preferably added to the latex in emulsion or dispersion form. Nonsoiling phenolic antioxidants such as 2,6-ditertiary-butyl-p-cresol, 4,4'-butylidene-bis (fi-t-butyl-m-cresol), 4,4'-thio-bis-(3-methyl-6-tbutylphenol), 2-5'-di-t-amylhydroquinone are particularly suitable for polychloroprene protection.

These rubbers also have very good mechanical properties, better than those of sulfuror diallc'ylxanthogen disulfide-modified polychloroprenes which have not been peptized in a latex state during their manufacture. An increase ranging from 10 to of tensile and tearing strengths is noted. Thereby they have the important property of being reduced on mixing machines during their use without the necessity of adding a pepetizing agent. Moreover the absence of thiurams in these sulfur-modified rubbers permits the manufacturer a large choice of vulcanization systems, allowing these rubbers to be used in different ways, the more so because this process results in a Mooney viscosity range generally used: from 20 to more than 150 and a crystallization rates range of polychloroprene.

Instantaneously peptized polymers having too high Mooney viscosities, can be treated during their use by peptizing agents that react on dry rubber. Thus, desirable Mooney viscosity ranges can be obtained.

The following examples illustrate the present invention in which indications of parts and percentages are by weight, but are not limitating thereof.

EXAMPLE 1 A sulfur-modified polychloroprene latex is prepared by the following aqueous emulsion composition:

Monomer phase: Parts by weight Chloroprene 100 Disproportionated resinous acid 4.0 Sulfur 0.35 Diisopropylxanthogen disulfide 0.40 Aqueous phase:

Deaerated water 150 Sodium hydroxide 0.8 Distabex LS (trademark of Socit Francaise des Matieres Colorantes, polymerized organic sulfonic salts) 0.7 Anhydrous trisodium phosphate 0.3

Catalyst solution:

Potassium persulfate 1 0.052 Deaerated water 1 3.51

Total added quantity.

Polymerization is effected at 45 C. under an ammonia atmosphere at a pH of 12.9 and the catalyst solution is added continuously to give a uniform polymerization rate.

The polymerization is stopped when about of the monomer has been polymerized by adding 0.01 part of p-tert-butyl catechol and 0.01 part of phenothiazine in an emulsion. 0.35 part of pure n-dodecyl-mercaptan is introduced into the latex as soon as the polymerization has stopped, the latex being under stirring. Then it is cooled and treated with steam to remove the residual chloroprene. After polymer isolation, Mooney consistency ML 1+4 at C. gives the value 46. The polymer obtained in the same manner but without the mercaptan addition, has a Mooney viscosity equal to 100.

EXAMPLE 2 Sulfur-modified polychloroprene latexes are prepared with the aqueous emulsion of Example 1 to which the following modifications were made:

TABLE I Diisopro- Mooney Polymer Reference py viscosity ization polychloroxanthogen n-Dodecyl- (ML 1+4 temd. prene ulfur disulfide mercpatan at 100 0.) C.-

Corresponding Mooney viscosities, obtained on the same polymers prepared without the addition of peptization agents ranged from to 80.

Polychloroprenes prepared as described above are odorless, have a pale color and after mixing have the properties mentioned in Table II, this being after vulcanization by the following formula:

5 6 TABLE H Rupture strength, kg./cm. -3 231 [Vulcanizates properties (after 40 minutes of vulcanization at 153 0.)] Modillus at 300% of elonganon 132 Tearing strength, kg./cm. 61 g fgigg Increase of IRH hardness at -5 C. after remainllgglg; at 5 0. rm 5 111g B. rema I] 1'1 0 Polychlo- Rupture of elonga Tearing r 1 day 1 rotprene (kstrfngtg (k Itiog (kstlreng igh d 1 d 3 d 14 3 days 3 1'8 erence g. cm. g. cm. g. cm. 5 ay ays BYS EXAMPLE 6 243 122 68.5 0 29 3?; 132 g 28 10 A latex is prepared under the same conditions as in 233 105 1 7 22 28 Example 1, by using 0.425 parts of diisopropylxanthogen 53 g 2g g g: 31 disulfide. When polymerization stops, 0.5 parts of the 245 111 64 2g 33 :1: sodium salt of mercaptobenzothiazole are added. 220 125 65 0 0 2 Then the latex is cooled and steam-treated so as to 235 88 61 6 24 251 130 615 34 M remove residfual chloroprene. After lsolatmg the polymer, measuring 0 Mooney consistency ML 1+4 at 100 C. 5 According to U.S. standard ASTM D 624-54 sample B. gives the value 39' EXAMPLE 3 After having vulcanized by the formula of Example 2, Sun-unmodified polychlomprene latexes are prepared for 40 m1nutes at 153 C., the following vulcanlzate with the aqueous emulsion of Example 1 to which the P p were measured: following modifications have been made: Rupture Strength 2 2 5 Modulus at 300% of elongation, kg./cm. 130 Plymers Tearing strength kg./cm. 63 Modifications XI XII Increase IRH hardness at 5 C. after remaining Diisopropylxanthogen disulfide 0.350 0.425 n-Octylmercaptan 0.300 0.225 1 day 1 3 days 4 Properties measured according to Example II are: 14 days 26 Increase of IRH hardness Mooney Modulus at 5 C. after remaining Reference viscosity Rupture at 300% of Tearing iorpolychloro- (ML 1+4 at strength elongation strength prene 100 C.) (kg/em (kgJcmJ) (kg/cm!) 1 day Sdays 14 days XI 59 235 108 07 1 12 a0 XII 48 233 110 62. 5 1 4 25 '1 According to U.S. standard ASTM D624-54 Sample B.

EXAMPLE 4 EXAMPLE 7 gl g' l sgii gg g i g afi gf g g i i zg ifig A latex is prepared under the same conditions as in followin 3 difications have been g; Example 1, but with 0.10 part of sulfur and 0.55 part g of diisopropylxanthogen disulfide. Polymerization is con- Polymers ducted at C. When polymerization stops, 0.10 part of the sodium salt of mercaptobenzothiazole is added. Modlficatlons XIII XIV XV Then the latex is cooled and steam-treated so as to re- Diisopropylxanthogen disulfide-... 0. 450 0.450 0.450 move residual chloroprene. After polymer isolation, -figiggg3ggg g E- 11-400 (1200 M00 measuring of Mooney consistency ML 1+4 at 100 C. added to thelatexwmm 45 34 16 gives the value 51. The polymer obtained in the same ratio at the polymerization 85 85 85 manner, but without an addition of sodium mercaptop benzothiazole salt has a Mooney viscosity of under The measured properties are as follows:

the same conditions of measuring.

Mooney Modulus Increase of IRH viscosity Rupture at 300% of Tearing hardness at 5 0. Reference poly- (ML 1+4 strength elongation strength chloroprene at C.) (kg/cm!) (kg/cmfi) (kg./cm. 1 day 14 days B According to U.S. standard ASTM D 624-54 sample B.

EXAMPLE 5 After having vulcanized by the formula of Example 2, for 40 minutes at 153 C., the following vulcanizate properties were measured:

Rupture strength, kg/cm. 250 Modulus at 300% of elongation, kg./ :m. Tearing strength, kg./cm. 69 Increase of IRH hardness at -5 C. after remaining for- 1 day 4 3 days 22 7 EXAMPLE 8 Sulfur-modified polychloroprene latexes are prepared by means of the aqueous emulsion of Example 1 to which the following modifications have been made:

1 Introduced into the latex just after the end of polymerization.

Mechanical properties of rubbers prepared by isolation of such latexes are excellent and vary according to conversion ratio, as is shown in the following table (after having vulcanized for 40 minutes at 153 C., with the formula of Example 2).

Sulfur-modified polychloroprene latexes are prepared by means of the aqueous emulsion of Example 1 to which the following modifications are made:

Diisopropylxanthogan disulfide is replaced by iodoform and n-dodecyl-mercaptan by the sodium salt of mercaptobenzothiazole:

Polymer XIX XX Conversion ratio (percent) 70 70 Polymerization temperature C.) 40 40 Sulfur (parts/100 parts by Weight of chloroprene) 0. 1 0. 35 Iodoform (parts/100 parts by weight of ehloroprene).. 0. 2 0. 2

Sodium salt of mercaptobenzothiazole 1 (parts/100 parts by weight of chloroprene) 0. 2

1 Intoduced into the latex just after the end of polymerization.

Properties of these rubbers measured after having vulcanized by the formula of Example 2 for 40- min. at 153 C., are shown in the following table:

8 Mooney viscosities of polymers XIX and XX measured before adding the sodium salt of mercaptobenzothiazole are respectively equal to and 85.

EXAMPLE 1o Sulfur-modified polychloroprene latexes are prepared by means of the aqueous emulsion of Example 1 to which the following modifications have been made: n-dodecylmercaptan is replaced by the following peptizing agents.

Amount introdueed (parts/ parts by Mooney visweight of eosity (ML Peptizing agent chloroprene) 1+4 at 100 C.)

Sodium isopropylxanthate 1 71 2-mercapto-benzimidazole l 67 Thiol benzene 0. 5 17 Sodium mereapto succinate. 1 76 Thio-2 naphtol 0. 5 20 It will be obvious to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is described in the specification.

What is claimed is:

1. A process for the instantaneous peptization of polychloroprene latexes, comprising polymerizing the chloroprene monomer in the presence of sulfur and a modifying agent selected from the group consisting of iodoform and the dialkylxanthogen disulfides, and peptizing the latexes at a pH at least equal to 9, by adding n-octyl mercaptan, n-dodecyl mercaptan, amylmercaptan or t-butylmercaptan.

2. A process according to claim 1 wherein the thiol addition is conducted at the end of the polymerization.

3. A process according to claim 1 wherein the pH is from 11 to 13.

4. A process according to claim 1 wherein the ratio of thiol added is from 0.05 to 10 millimoles per mole of chloroprene monomer.

5. A process according to claim 1 wherein the ratio of sulfur added is from 0.01 to 2% by weight based on the chloroprene monomer.

6. A process according to claim 1 wherein dialkylxanthogen disulfide is the modifying agent added in a ratio of 0.5 to 4 millimoles per mole of chloroprene monomer.

7. A process according to claim 1 wherein iodoform is the modifying agent added in a ratio of from 0.1 to 4 millimoles per mole of chloroprene monomer.

8. A process in accordance with claim 1 wherein said modifying agent is diisopropylxanthogen disulphide.

Increase of IRH vlggggiy Ru w Modaius at hardness at 5 C. Polychloroprene (ML 1+ Stl'llglfl? eion gi rl siliiii il 3:1 Iemammg reference at 100 C.) (kgJcmJ) (kg. cm. (kg/cm. 1 day 3 days XIX-. 50 XX... 60 323 iii 98 i 33 References Cited UNITED STATES PATENTS 2,227,518 1/ 1941 Starweather 260-923 2,234,211 3/1941 Walker 26092.6 2,234,215 3/1941 Youker 260-923 3,595,847 7/1971 Mayor-Mader 260-923 FOREIGN PATENTS 801,426 9/1958 Great Britain 26092.3 959,122 5/1964 Great Britain 26092.3

' US. Cl. X.R.

zen-29.7 so. 45.7 s, 45.95, 79.5 c 

